1. Field of the Invention
This invention relates to a method for correcting color data during color data transmission from a pickup device to an output device.
2. The Prior Art
The above-mentioned method for color data correction has special importance in the context of digital image processing, since colored digital images are ordinarily transmitted from individual pickup devices to one or more display or output devices using red, green, and blue image points (RGB pixels). The same applies to digital moving pictures and digital films. In this connection, the intensities of red, green, and blue in each pixel are controlled to produce different colors in the sense of additive color mixing.
In display or printing technology, for example with monitors as display or output devices, the color mixing is achieved by individual small, differently colored dots lying so close to one another that their images are superimposed on the retina of a human eye by its limited resolution. Conventional pickup devices such as scanners or color CCD cameras often make use of three CCD chips with preceding color filters for color pickup, so that a separate CCD array is available for each of the three primary colors RGB (red, green, and blue).
However, video or digital cameras that operate with a single CCD sensor, which detects the individual colors using preceding strip filters or mosaic filters, are far more common since the individual pixels or image points of the CCD chip usually have no differentiating color sensitivities by themselves, but usually detect gray values and their intensity. In other words, the particular color information at this point is made available by an appropriately configured preceding color filter or a mosaic filter or strip filter.
The particular pickup devices that use CCD sensors, in the same way as display devices, for example monitors or printers, modify the colors transmitted to them equipment-specifically in each case. In other words, the color, not the color information, is changed, for example because of the particular phosphor used. The lighting of an object to be imaged also plays a role. While the maximum sensitivity of the human eye is in the green wavelength region at about 555 nm, semiconductor cameras, for example, are most sensitive in the near infrared region at wavelengths of about 700 nm to 800 nm. This is taken care of in practice by a rough color correction by providing that a suitable color filter matched to the sensitivity of the eye is placed ahead of the pickup device in question.
In addition to this, computational methods of image processing are used to allow corresponding filter functions to be represented digitally, or to make a color data correction. To provide for the most correct possible exchange of color data that is best adapted to human color perception and that best takes into account the relative color separations during color data transmission from the particular pickup device to the output device, a number of IT firms have agreed in the past on a common standardized color correction calculation that is prescribed by the authoritative “International Color Consortium” (ICC) (more detailed information in this regard can be found at the internet address www.color.org.).
A so-called standard color space is defined in the known color correction calculation. To obtain the standard color values to be used with it, it is necessary, for example, for the manufacturer to determine the specific color perception characteristics of a CCD camera as a pickup device, and to take them into proper consideration, and to include in the calculation the individual color reproduction characteristics of a monitor (of the phosphors) as the output device.
The standard color space mentioned is independent of the pickup device and of the output device, with only the input color data of the pickup device and the output color data for the output device undergoing a corresponding device-specific transformation. In this way, practically any desired pickup device can be combined with any desired output device, because there is always reference back to the conforming standard color space. The detected color data are subjected to a color correction calculation to become the standard color values of the standard color space, and these standard color values in turn are subjected to another color correction calculation to take into account the instrument specifications of the output device. This procedure has proved itself.
However, since the described ICC method or other method of calculation for color correction is always applied to all of the RGB color values and RGB color pixels of the associated pickup device, the processing rate is often slow. For example, a CCD chip with 1 million pixels as the pickup device consistently also obtains 1 million color pixels, which may contain only partial color information—corresponding to the particular front-end color filter—and are transformed into the 1 million color pixels only by the camera followed by interpolation. These color pixels are subjected to the color correction calculation according to the described ICC method. Because of this, it has not yet been possible to subject color data received by a pickup device directly to the described color correction calculation with consideration of a somewhat high resolution of the pickup device, and to output it to an associated output device with almost no delay. Actually, delays between pickup and reproduction have to be expected, which does not permit immediate observation on the specimen, for example, of cell motions or cell growth it the course of a simple search. Instead, it has been necessary up to now first to record a video with adequate imaging rate and then to interpret it. The invention is intended to be of assistance here.